Unbiased segregation of fission yeast chromosome 2 strands to daughter cells

Abstract

The base complementarity feature (Watson and Crick in Nature 171(4356): [737][738] 1953) and the rule of semi-conservative mode of DNA replication (Messelson and Stahl in Proc Natl Acad Sci U S A 44: [671][672][673][674][675][676][677][678][679][680][681][682] 1958) dictate that two identical replicas of the parental chromosome are produced during replication. In principle, the inherent strand sequence differences could generate nonequivalent daughter chromosome replicas if one of the two strands were epigenetically imprinted during replication to effect silencing/expression of developmentally important genes. Indeed, inheritance of such a strand-and sitespecific imprint confers developmental asymmetry to fission yeast sister cells by a phenomenon called mating/cell-type switching. Curiously, location of DNA strands with respect to each other at the centromere is fixed, and as a result, their selected segregation to specific sister chromatid copies occurs in eukaryotic cells. The yeast system provides a unique opportunity to determine the significance of such biased strand distribution to sister chromatids. We determined whether the cylindrical-shaped yeast cell distributes the specific chromosomal strand to the same cellular pole in successive cycles of cell division. By observing the pattern of recurrent mating-type switching in progenies of individual cells by microscopic analyses, we found that chromosome 2 strands are distributed by the random mode in successive cell divisions. We also exploited unusual "hotspot" recombination features of this system to investigate whether there is selective segregation of strands such that oldest Watsoncontaining strands co-segregate in the diploid cell at mitosis. Our data suggests that chromosome 2 strands are segregated independently to those of the homologous chromosome.

Cosegregation of asymmetric features during cell division

“…By contrast, no preferential segregation of chromosomes II and III could be detected (table 3). Consistently, a previous study examining the distribution of chromosome II also concluded that it segregates randomly between the two daughter cells [42]. Similar conclusions were drawn when stricter ranges were used, such as theoretical value ±0.025 (data not shown).…”

A Unique DNA Recombination Mechanism of the Mating/Cell-type Switching of Fission Yeasts: a Review

“…Thus, the hotspot recombination is proposed to occur through a pathway other than the conventional DSB repair model. In support of this hypothesis, the hotspot recombination is not reduced in the swi5 mutant, encoding a function required for general mitotic recombination in yeast (65).…”

“…A recent study (65) has reported several unusual features of the mechanism of hotspot recombination: (i) recombination occurs in the S/G2 phase of the cell; (ii) recombination occurs at an appreciable rate in about 4.0% of cell divisions; (iii) one-half of recombination events causes homozygosis, while the other half only changes linkage of markers flanking the mat1 locus; (iv) recombination occurs only between previously imprinted nonsister chromatids; and (v) recombination occurs only between chromatids that simultaneously contain DSBs/nick. These results support the armsswapping model (Fig.…”

Asymmetric Centromeres Differentially Coordinate with Mitotic Machinery to Ensure Biased Sister Chromatid Segregation in Germline Stem Cells

“…More than four decades ago, an ''immortal strand'' hypothesis proposed that stem cells could retain ''immortal'' DNA strands (Cairns, 1975) to minimize the incidence of mutations, which may arise during pathological progression or aging. However, later in vivo studies using more rigorous methods and precise labeling have challenged this hypothesis (Klar and Bonaduce, 2013;Sauer et al, 2013;Schepers et al, 2011;Yadlapalli and Yamashita, 2013). On the other hand, examples of biased chromosome segregation have been reported in multiple stem cell systems, including both invertebrates and vertebrates (Rocheteau et al, 2012;Yadlapalli and Yamashita, 2013).…”